Report ignorefile location when no content added

Users have accidently had a .containerignore or .dockerignore
file in their context directly which blocked all content.
Currently we report that no globs matched, but do not
identify where the globs came from.

This change is an attempt to add this data to the error.
Example: #3318

Signed-off-by: Daniel J Walsh <dwalsh@redhat.com>

add.go

@@ -564,7 +564,17 @@ func (b *Builder) Add(destination string, extract bool, options AddAndCopyOption
 			}
 		}
 		if itemsCopied == 0 {
-			return errors.Wrapf(syscall.ENOENT, "no items matching glob %q copied (%d filtered out)", localSourceStat.Glob, len(localSourceStat.Globbed))
+			ignoreFile := filepath.Join(contextDir, ".containerignore")
+			if _, err := os.Stat(ignoreFile); err != nil {
+				ignoreFile = filepath.Join(contextDir, ".dockerignore")
+				if _, err := os.Stat(ignoreFile); err != nil {
+					ignoreFile = ""
+				}
+			}
+			if ignoreFile != "" {
+				ignoreFile = " using " + ignoreFile
+			}
+			return errors.Wrapf(syscall.ENOENT, "no items matching glob %q copied (%d filtered out%s)", localSourceStat.Glob, len(localSourceStat.Globbed), ignoreFile)
 		}
 	}
 	return nil

tests/bud.bats

@@ -110,6 +110,7 @@ symlink(subdir)"
 @test "bud with .dockerignore #2" {
   run_buildah 125 build -t testbud3 --signature-policy ${TESTSDIR}/policy.json ${TESTSDIR}/bud/dockerignore3
   expect_output --substring 'error building.*"COPY test1.txt /upload/test1.txt".*no such file or directory'
+  expect_output --substring "${TESTSDIR}/bud/dockerignore3/.dockerignore"
 }
 
 @test "bud-flags-order-verification" {